1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, an electrophotographic process cartridge and an image forming apparatus and, more particularly, to an electrophotographic photoreceptor which has high wear resistance and high heat resistance and also exhibits low torque to a cleaning blade, and an electrophotographic process cartridge and an image forming apparatus using the same.
2. Description of the Related Art
Heretofore, polycarbonates have widely been used as a binder resin which is applied to a surface layer and a charge transport layer of a multi-layer type electrophotographic photoreceptor comprising plural functional layers which are mutually laminated. Among these polycarbonates, bisphenol Z type polycarbonate has occupied on important position as a binder resin for a charge transport layer because of its high solubility in various organic solvents in the preparation of a coating solution as well as its comparatively excellent mechanical strength and electrical characteristics for a charge transport layer, as described in Japanese Patent Application Laid-Open (JP-A) No. 1-246580.
JP-A No. 6-75391 reports an attempt to apply a bisphenol A type polycarbonate and various modified polycarbonates, which were inferior in solubility in an organic solvent in the prior art, for the purpose of extending the lifetime of an electrophotographic photoreceptor. Also JP-A No. 2003-43817 reports an attempt to apply various polyallylates which were inferior in electrical characteristics. JP-A No. 8-123049 reports an attempt to improve solubility by copolymerizing a polycyclic aromatic polycarbonate, which is only slightly soluble in a solvent, with a bisphenol type polycarbonate.
However, high image quality equivalent to that of printing has recently been required in electrophotography, and since cleaning has been intensified in order to completely remove deposits and residual toners on an electrophotographic photoreceptor, a surface layer of the electrophotographic photoreceptor requires higher wear resistance and lower torque than those of the prior art. Thus, it has become impossible to satisfy these requirements using the prior art. With size reduction of printers, a distance between the electrophotographic photoreceptor and a heat-generating unit such as a fixing device has decreased. Thus higher heat resistance is required of the electrophotographic photoreceptor, and it has become impossible to satisfy higher heat resistance using the prior art.
With regard to polycarbonate, a toxic substance such as phosgene is used as a synthetic raw material thereof, and thus improvement of the process is required. Since a large amount of an organic solvent is used to prepare a coating solution of the polycarbonate, the organic solvent must be disposed of, which is not preferable. Molecular design for increasing the mechanical strength of polycarbonate increases the hardness, but also makes the polycarbonate brittle. Thus solvent cracks may occur when the electrophotographic photoreceptor containing the molecular designed polycarbonate is used for a long period.
Further, in the manufacture of the electrophotographic photoreceptor, a solution prepared by dissolving a functional material in an organic solvent is often applied by a dip coating method or a spray coating method. The use of a large amount of the organic solvent increases environmental burden.